Part of a 19-bug update that addresses vulnerabilities in Windows, IE9, Excel and .Net

Microsoft today patched 19 vulnerabilities in Windows, Internet Explorer 9 (IE9), Excel and the .Net development framework, including four flaws in the just-released Windows 8 and its tablet spin-off Windows RT.

Of Tuesday's six security updates, four were labeled "critical," Microsoft's most-severe threat ranking, while the remaining pair were pegged as "important" or "moderate." Of the 19 vulnerabilities patched today, seven were tagged as critical.

"The IE9 [bulletin] is the one that should be patched first," said Andrew Storms, director of security operations at nCircle Security, in an interview today. "It's a drive-by," he added, referring to the tactic that only requires hackers to trick users into browsing to a malicious website.

Doing that with an unpatched copy of IE9 could result in a successful hijacking of a Windows 7 or Vista PC. IE9 only runs on those two operating systems.

No other versions of Microsoft's browser, including the new IE10, were affected by MS12-071. IE10 is bundled with Windows 8 and Windows RT, and today shipped as a "Release Preview" for Windows 7.

That update patches three vulnerabilities in Windows kernel mode drivers, one of which was labeled critical. The latter was a bug in the operating system's parsing of TrueType fonts, which could be exploited only by determined attackers, said Storms.

"Despite the fact that it looks nasty, it's not very realistic to expect working exploits," argued Storms, ticking off the many requirements for a successful attack, including the need to spoof a proxy server.

Microsoft rated the bug as "2" on its exploitability index, the company's threat estimate, essentially agreeing with Storms. "Exploit code would be difficult to build," Microsoft said of the TrueType bug.

That vulnerability was reported to Microsoft by Google's bug bounty program. In late September, Google paid a pair of researchers $5,000 for rooting out the vulnerability, part of a $29,500 payday for nine different researchers.

The two critical flaws in MS12-072 were pegged for Windows 8 and its offspring, as was the TrueType font bug in MS12-075 and one of the vulnerabilities in MS12-074, which patched all versions of the .Net framework.

"I'm sure Microsoft is disappointed to have released Windows 8 in late October and have already issued patches for it," said Storms. "But truth be told, a lot of code is reused, and it shouldn't be surprising to see bug fixes in Windows 8. Despite all the hype about newer platforms being the most secure, bugs will be found and bugs will be fixed."

November's six security updates can be downloaded and installed via the Microsoft Update and Windows Update services, as well as through WSUS.